The proposed research is directed towards determining the modes of excitation and of excitation-contraction coupling utilized by different blood vessels during stimulation by various types of vasoconstriction agents. In particular, the research seeks to determine the role of ions in these processes and the effects of alterations of the ionic environment on them. The approach involves simultaneous measurements of force development and electrical activity in a number of mammalian arteries following the application of adrenergic and non-adrenergic agonists. In addition flux studies directed towards determining the source of activator calcium will be made. Additionally certain in vitro findings will be re-examined in vivo by observing the effects of altering external ion concentrations on the changes in vascular resistance induced by the intra-arterial infusions of the various vasoconstrictor agents.